Timing on a 1991 nissan 300zx

There is no means of setting the timing if you are referring to a conventional timing light. The engine is designed with sensors that sense the angle of the camshafts in relationship to the crankshaft and whether it is on the intake or exhaust stroke on the #1 cylinder. This design is actually a little more complex than that because it has variable valve timing which means that the angle in which the camshafts open and close the valves, change with RPM's This give the engine the best of both worlds. It's like have an engine with cams designed for torque at low RPM and a set of cams designed for HP with a free breathing quick revving engine you would have on a race course. The ECM is constantly changing the timing and injector pulse width based on many sources of input, from, the O2 sensor, air flow, air temp, coolant temp, fuel pressure, RPM's and a host of other inputs.
SO>>>>>>>>>>>> in a manner of speaking, unless you are making reference to setting up the timing chain, everything else is under control by the ECM and related components.